An ink jet recording system is a system wherein fine droplets of ink are jetted and deposited onto a recording medium such as paper sheet or film transparency. The droplets are deposited in such a manner as to generate pictorial images or symbols such as alphanumeric characters. Ink jet recording systems offer many positive features compared to previous imaging systems in that these systems are typically, performed at high speed, noiseless, with no further chemical development or fixing required, reproducible, inexpensive, and can produce either monotone or full color renditions. Furthermore, under appropriate conditions the quality of the ink jet image is comparable to photographic pictures but can be formed in a single step without the need for toxic chemicals. Lastly, if changes to the final imaged copy are required, it is relatively simple to make corrections within the stored computer information that is then outputted to the printer to rapidly print a new copy. Such a turnaround using conventional photographic processes would require elaborate and multiple steps.
The rendition or image generated by the ink jet process must meet stringent criteria if it is going to be of significant commercial value. These criteria include: high printed dot density (optical density), bright and true colors (chroma), and rapid absorption of ink even in areas where multiple inks are required to prevent running or blotting. Additionally, the edges of the printed dots must be sharp, and the images themselves must be waterfast and should not fade with time. Three elements dictate the final quality of the ink jet image; the hardware system that generates the ink droplets, the ink receiving (recording) media and finally the ink itself. Depending on the specific criteria of concern one or more of these elements may need to be optimized.
With regard to the concern for waterfastness and light induced fading, the two most critical elements are the recording media and the ink formulation. Because of environmental and health concerns it has been desirable to use aqueous formulations for ink jet inks and therefore, for compatibility reasons, hydrophilic type recording media are often employed. Although this system can address the health and environmental concerns by providing a relatively low toxicity ink media, it causes the imaged recording medium to be problematic to subsequent contact with moisture, specifically the media itself is prone to tackiness or blocking and the imaged inks will tend to "bleed" and not be waterfast. Since the ink formulations are aqueous based, the colorant/dye within the aqueous formulation must themselves have high water solubility. To achieve this characteristic, low molecular weight organic dyes having solubilizing groups were typically selected. Water insoluble pigments have also been used but have special problems such as clogging of nozzle jets and low chroma in the printed image. As already mentioned these dyes have significant water solubility and if there are no strong binding forces holding the dye to the receiver medium then the dye will partially redissolve or completely enter the liquid aqueous phase and diffuse and "bleed" or "run off" the recording media when the image is wet inadvertantly or upon exposure to outdoor environment, or under high humidity conditions. The resulting image smear or complete loss of image is unacceptable for many applications. Another long standing problem known in the industry is that low molecular weight organic dyes are known to degrade especially on exposure to light and air. This degradation is accelerated when dyes are deposited on a receiving media where the dye is exposed over a large surface area. Typically this phenomenon of "light induced fade" or oxidative degradation of these dyes occurs over a period of time. Obviously these characteristics, water and light fastness, are readily apparent to the customer and are highly desirable. This is especially so for media that is intended for outdoor exhibition.
Efforts to enhance waterfastness and improve image quality by lowering dot spread have often employed dye mordants such as cationic polymers. These mordants fix the dye to the ink receptive layer and fix the dye close to the site at which the inkjet drop has been deposited. Unfortunately, while enhancing waterfastness mordanting often this results in a decrease in the light stability of the dye, see for example "Effects of Mordant Type and Placement on Inkjet Receiver Performance", L. Shaw-Klein, Final Program and Proceedings of IS&T NIP14:International Conference on Digital Printing Technologies (1998). It is further known in the ink jet technology literature, see U.S. Pat. No. 4,371,582, that anionic dyes can be fixed or mordanted to cationic latices via coulombic or electrostatic bonds. However the '582 patent does not disclose the simultaneous binding of dyes and stabilizers to the same latex particle nor does it teach what benefits would derive from such a combination.
The light induced fading of dyes is a well known problem in a variety of technologies such as textiles and more recently in ink jet reproductions. This defect has inhibited the growth of ink jet technology into the display market which requires the exposure of ink jet prints to both indoor and outdoor lighting for long periods of time, see for example "Permanence of Ink-Jet Prints: A Multi-Aspect Affair", M. Fryberg et al., Final Program and Proceedings of the Imaging Science and Technology (IS&T) Non Impact Printing (NIP) 13: International Conference on Digital Printing Technologies (1997)", herein incorporated by reference in its entirety. Incorporating antioxidants and UV absorbers directly into an ink receiving layer has been disclosed, see for example U.S. Pat. No. 4,680,235. This approach however is inferior to the current invention which causes the dyes and stabilizers to remain proximate due to complexation, since in the case of the prior art, dye and stabilizer only interact infrequently and solely by random chance. The use of antioxidant hindered phenols, see U.S. Pat. No. 5,096,456, and metal complex stabilizers, see U.S. Pat. No. 4,655,785, to improve the lightfastness of dyed textile fibers is known in the prior art. In the ink jet prior art, increased efficiencies of light stabilization are reported to be afforded when a stabilizer is proximate to the dye, see for example U.S. Pat. No. 5,643,356, column 16, lines 40-45 and example 11, herein incorporated by reference in its entirety. In the '356 patent, the technology employs a stabilizer covalently bound to a cyclodextrin via a chemical reaction, and then binding a dye to the modified cyclodextrin via an inclusion complex.
Having now disclosed the relevant problems associated with the current state of ink jet technology and the need for solutions to these problems the present invention will be described.